Thermoresponsive polymers based on ring-opening metathesis polymerization†
A series of novel thermoresponsive polymers were developed with hydrophobic polynorbornene backbones and hydrophilic N-alkyl-amide/imide side groups. The preparation method was built on the combination of ring-opening metathesis polymerization (ROMP) and activated ester click chemistry. The polynorbornene templates (P1, P2 and P4) were synthesized by ROMP having pentafluorophenyl ester side groups. The various amine agents were then used to post-modify the precursors of P1, P2 and P4 by a nucleophilic substitution of activated esters, producing a library of well-defined N-alkyl-amide/imide polynorbornenes (P1a–h, P2a–h and P4a–h). The thermoresponsive properties were systematically investigated and quantified by turbidity measurements. By manipulating the types and densities of hydrophilic N-alkyl-amide/imide side groups to balance the hydrophilicity/hydrophobicity of the resultant polynorbornenes, their cloud point temperature (Tcp) in water could be tuned in a wide temperature range between 14.4 °C and 97.6 °C.